1. Field of the Invention
The present invention relates to abrasive powders and slurries containing the powders, as well as chemical mechanical planarization processes utilizing the slurries. In particular, the present invention is directed to such powders and slurries wherein the abrasive powder has a small average particle size, controlled particle size distribution, spherical morphology and is substantially unagglomerated.
2. Description of Related Art
Slurries consisting of abrasive and/or chemically reactive particles in a liquid medium are used for a variety of polishing and planarizing applications. Some applications include polishing of technical glass, magnetic memory disks, native silicon wafers and stainless steel used in medical devices. Chemical-mechanical planarization (CMP) is a method to flatten and smooth a workpiece to a very high degree of uniformity. CMP is used in a variety of applications including polishing of glass products such as flat panel display glass faceplates and planarization of wafer-based devices during semiconductor manufacture. In particular, the semiconductor industry utilizes CMP to planarize dielectric, metal film as well as patterned metal layers in the various stages of integrated circuit manufacture.
CMP consists of moving a nonplanarized, unpolished surface against a polishing pad at several PSI of pressure with a CMP slurry disposed between the pad and the surface being treated. This is typically accomplished by coating the pad with a slurry and spinning the pad against the substrate at relatively low speeds. The CMP slurry includes at least one of two components: an abrasive powder for mechanical action and solution reactants for chemical action. The solution reactants are typically simple complexing agents or oxidizers, depending on the materials to be polished, and acids or bases to tailor the pH. For polishing metal layers, the slurry will predominately polish the metal through the action of the solution reactants. The abrasive powder is primarily responsible for the mechanical abrasion at the surface, but can also contribute to the chemical action near the surface.
As the powder abrades the surface, protrusions and other irregularities are removed. The chemical species in the slurry can perform different functions, such as aiding in the dissolution of the mechanically removed material by dissolving it into solution or oxidizing the surface layers to form a protective oxide layer. The particular solution chemistry is primarily dependent upon the material being worked upon. The presence of an abrasive material, however, is common to all CMP slurries.
Conventional abrasive powders are hard agglomerates (i.e. aggregates) typically with an average aggregate size of less than about 1 xcexcm in diameter. The particles are typically agglomerates of smaller particles having an irregular shape, which decreases the performance of the slurry. Larger non-spherical particles and particle agglomerates in the slurry result in scratching of the surface as well as uneven and unpredictable polishing rates. As a result, semiconductor device manufacturers are forced to dispose of a significant number of defective devices, increasing the production cost.
CMP slurries can be placed into categories based on the materials to be polished. Oxide polishing refers to the polishing of the oxide or interlayer dielectrics in integrated circuits, while metal polishing is the polishing of metal interconnects (plugs) in integrated circuits. Silica (SiO2) and alumina (Al2O3) are most widely used as abrasives for metal polishing, while silica is used almost exclusively for oxide polishing. Ceria (CeO2) is also used for some applications, including metal polishing and polymer polishing.
Many examples of CMP processes are illustrated in the prior art, particularly slurries for use in CMP. For example, U.S. Pat. No. 4,910,155 by Cote et al. discloses a chemical mechanical polishing process for planarizing insulators wherein a slurry of particulates at an elevated temperature is disposed between a rotating polish pad and the insulator surface to be polished. U.S. Pat. No. 4,954,142 by Carr et al. discloses a chemical mechanical polishing method including the use of a slurry comprising abrasive particles, a transition metal chelated salt and a solvent for the salt. The salt selectively etches certain features, such as copper vias, on the surface of an electronic component substrate.
U.S. Pat. No. 5,209,816 by Yu et al. discloses a semiconductor planarization method particularly useful for aluminum containing metal layers. The method includes the use of a mechanical polishing slurry comprising phosphoric acid and hydrogen peroxide. The hydrogen peroxide is an oxidizing agent that oxidizes the aluminum to alumina, which is subsequently etched by the phosphoric acid. U.S. Pat. No. 5,225,034 by Yu discloses a semiconductor planarization method particularly useful for planarization of copper containing layers. The method utilizes a slurry which includes at least one of HNO3, H2SO4 and AgNO3.
Some work has been directed to the tailoring of the abrasive particle component. For example, U.S. Pat. No. 5,264,010 by Brancaleoni et al. discloses an abrasive composition for use in planarizing the surface of a work piece, wherein the abrasive portion includes 30 to 50 weight percent cerium oxide, 8 to 20 weight percent fumed silica and 15 to 45 weight percent precipitated silica. It is disclosed that the combination of the three types of abrasive provides good planarization.
U.S. Pat. No. 5,527,423 by Neville et al. discloses a slurry for use in chemical mechanical polishing of metal layers. The slurry includes abrasive particles that are agglomerates of very small particles and are formed from fumed silicas or fumed aluminas. The agglomerated particles, typical of fumed materials, have a jagged, irregular shape. It is disclosed that the particles have a surface area of 40 to 430 m2/g, an aggregate size distribution less than about 1 xcexcm and a mean aggregate diameter of less than about 0.4 xcexcm.
U.S. Pat. No. 5,389,352 by Wang disclosed a process for preparing a chemically active oxide particle composed primarily of CeO2. The method includes forming an aqueous solution of a cerium salt and an oxidizing agent and aging the mixture for at least about 4 hours. The particle size of the powder was on the order of about 0.1 xcexcm. U.S. Pat. No. 5,429,647 by Larmie discloses a method for preparing an abrasive grain which includes both alumina and ceria.
U.S. Pat. No. 5,693,239 by Wang et al. discloses a CMP slurry which includes abrasive particles wherein about 1 to 50 weight percent of the particles and crystalline alumina and the remainder of the particles are less abrasive materials such as aluminum hydroxides, silica and the like.
Each of the foregoing U.S. patents is incorporated herein by reference, in their entirety.
Conventional CMP powders typically consist of agglomerated particles having an agglomerate shape that is inadequate for reproducible CMP performance. As a result, integrated circuit manufacturers scrap significant amounts of product due to defects formed during the CMP step. Furthermore, as integrated circuit dimensions continue to decrease in size, there will be an increasing demand for higher CMP performance and reliability, particularly for damascene and dual damascene structures.
Conventional CMP powders are produced using a flame combustion process which produces small particles that are highly agglomerated. These particles are commonly referred to as fumed. Due to the high degree of agglomeration, these particles have angular and irregular shapes which lowers the reliability of the CMP process by virtue of uncontrollable polishing and removal rates. The elongated and angular particles behave like miniature knife blades cutting into the surface of the integrated circuit. Non-spherical particles also tend to abrade the metal portions at too high of an abrasion rate.
There is a need for abrasive powders for CMP slurries that will permit better control over the planarization process. It would be particularly advantageous if such powders could be produced in large quantities on a continuous basis.